Note: Descriptions are shown in the official language in which they were submitted.
V~JLCl~NIZED RUBBER FOOl~ PRODUCT
Field of the Invention
~ his invention relates to rubber footwear
products and the manufacture thereof, and more particu-
larly to the manufacture of rubber footwear products
comprising a vulcanized assembly made from an uncured
rubber upper, insole, and midsole, in combination with
an outsole separately affixed to the midsole of the
vulcanized assembly.
Backqround of the Invention
In the conventional manufacture of rubber
footwear Droducts, uncured rubber or rubber coated
fabrics are typically milled or extruded into appropriate
thicknesses from which the desired sized component parts
for the footwear product are cut. The uncured components
are normally assembled upon a forming device such as a
metal last. The metal last bears the internal shape
and size of the desired footwear product. The last is
normally a heat conductive metal form such as a hollo~ed,
shoe or boot-shaped aluminum form. It is conventional
to assemble on the forming last an uncured rubber upper,
an uncured rubber insole, an uncured foxing band (e.g.
a flat uncured strip), an uncured rubber binder (e.g.
uncured sheeting stock or filler) and a precured rubber
sole, which has been coated upon the forming last, to
,~
Eorm a footwear assembly. This completed footwear
assembly is then vulcanized to provide the desired rubber
footwear vulcani2ed product.
An uncured, rubber shoe or boot upper is
typically positioned to adhesively overlap the insole
upon the last. An uncured foxing band or ~lat band
(e.g. 1-2 inches in width) is then placed around the
outer periphery or rim of the rubber upper. An uncured
binder or filler is then placed onto the insole. The
blnder or filler will not normally extend beyond the
exposed surface of the insole. An uncured rubber outsole
is then wrapped over the projecting edge of the insole
onto the uncured rubber upper above the feather lineO
This uncured rubber assembly, which has the appearance
of crude footwear, is then vulcanized upon the last,
typically for about 1 to 2 hours at temperatures ranging
from about 250-350F, to provide the vulcanized product.
The component parts are thereby chemically and physically
melded into a complete vulcanized footwear product of
unitary construction.
Uncured (unvulcanized) natural or synthetic
rubber footwear components normally possess sufficient
tack for assembly upon the forming last. An uncured
rubber formulation generally includes ethylenically
unsaturated polymeric substances in combination with
conventional vulcanization or curative additives.
Included amongst such conventional additives are cross-
linking agents such as sulfur, accelerators, tackifiers,
antioxidants, and activators. The additives and poly-
meric rubber substances are usually admixed in a Branbury
mixer and then formed into the desired thickness or
shape of the footwear component parts. This is usually
accomplished by milling, extruding, and calendering
techniques, without curing the rubber formulation.
Vulcanization of the uncured footwear assembly
alters the chemical and phy9ical attributes of the rubber
composition by crosslinking ethylenically unsaturated
~ 5~
polymeric linkages. Crosslinking occurs not only within
each of the individual assembled component parts, but
also between ethylenically unsaturated polymeric linkages
positioned at the interface of the adhesively overlapped
component parts. This melds the component parts into a
unitary, vulcanlzed product.
Heretofore, conventional manufacture of such
rubber footwear products has required vulcani~ation of
the entire footwear assembly. This requirement has
placed severe constraints ~pon the rubber footwear
manufacturing industry. ~hermoplastic and other natural
or synthetic polymeric substancés thermally sensitive
or degradable upon vulcanization are not acceptable for
~se in such a vulcanized product. Outsoles for such
footwear products are essentially limited to vulcanized
rubber outsoles. Such constraints have made it difficult
for the rubber footwear industry to effectively compete
against other footwear products capable of being produced
in more fashionable designs (e~g. high heeled shoes,
western boots, contrasting sole colors, etc.) at low
cost. Manufacture of products such as footwear of a
lightweight construction, replaceable or repairable
soles, specialty soles adap~ed for speci~ic uses (e.g.
spiked, cleated, or ridged soles for sports such as
golf, football, hiking, baseball, etc.) and products
having other specialty wear ~eatures is not ~easible
using existing rubber footwear manufacture technology.
It would be desirable to incorporate many of
the desirable attributes of such other, non-rubber
footwear products into a footwear vulcanizate while
retaining many of a vulcanizate's desirable attributes,
such as resistance to air, gas, sunlight, hydrocarbons,
moisture penetration, fats and oils, and acid and other
chemic~ls, together with its excellent durability,
strength, elasticity, electrical and heat insulating
properties, and structural inteyrity. A different
method of manufacturing rubber footwear products would
o~
be desirable if i~ could provide ~otwear products
uniquelv different in construction, utility and design
from conventional rubber footwear. Vulcanized rubber
footwear products able to separately receive an outsole
would afford significant labor, equipment, production
time and material savings. Notwithstanding a long felt
need for such rubber footwear products, the manufacture
of rubber footwear vulcanizates has remained essentially
unchanged since the beginnin~ of the 20th century.
Athletic sports footwear products (e.g. tennis
shoes, etc.) generally differ from products of vulcanized
rubber manufacture in that such sports footwear f-equently
include a polyurethane outsole. Such outsoles are
normally incorporated into the athletic footwear product
by injection molding. U.S. Patent No. 4,245,406, by
Landay, discloses a sport shoe having an outsole
comprised of an injection molded polyurethane midsole
to which a rubber outer sole is attached. Similarly,
U.S. Patent No. 4,455,765, by Sjosward, disclose, a
sport shoe product having an outsole with a polyurerhane
midsole and a rubber outer sole. A patenc issued to
Giese, U.S. Patent No. 4,366,634, discloses an injection
molded ~port shoe, such as a tennis shoe, having a rabric
upper portion secured to a sidewall and an outsole
constructed of two different materials (preferably ~ubber
and polyurethane midsole) to which a rubber outer sole
is bonded. Another variation involving polyurethane
shoe construction is disclosed by U.S. Patent No.
4,228,600 by Kruge. The Kruge shoe bottom comprises a
flexible, closed-cell, crosslinked polyolefin foam having
at least one surface of exposed open cells and an elasto-
meric polyurethane film which encompasses the foam.
A method for manufacturing a ski boot
constructed of an upper part and a prefabricated sole
is disclosed in U.S. Patent No. 3,273,263 by Kilma.
The prefabricated sole of the Kilma patent includes a
metal plate adapted to receive notched nails or screws
~ %~;~)25~-~
--5--
embedded ~ithin the sole. The sole is secured to the
ski boot by means of glue and nails or screws. In
another U.S. Patent by Denu, No. 4,130,947, a method of
making a sole is disclosed wherein a layered substance
resistant to abrasion is vulcanized onto a dampening
layer of a synthetic or na~ural rubber.
U.S. Patent 2,983,643 by Seiberling
discloses a heel ostensibly suitable for adaptation to
footwear constructed from leather uppers. Seiberling
mentions, at column 1, lines 25-3~, the difficulties
typically encountered when adhesively bonding a cured
rubber heel to another surface. According to
Seiberling, it is customary to abrade the skin surface
of the cured rubber to roughen it. Otherwise, the
cured skin becomes so slick that it does not form a
good bond with the adhesive. The roughened surfaces
of the cured rubbers may then be adhered to another
surface by an adhesive. Seiberling proposes to avoid
the need for roughening by incorporating cellulosic
fibrous materials into that portion of the heel
surface to the glued (e.g. by animal glue) onto the
shoe. This involves placing an uncured or raw rubber
biscuit with an overlying fibrous mat into a ~old,
then vulcanizing to form a heel vulcanizate having
embedded cellulosic fibrous projections upon the
glueing side.
A European patent speci~ication by Phillips
(Publication No. 0 075 ~61) further illustrates the
problem with repairing leather footwear using thermo-
setting butadiene-styrene half soles. Phillips propose~
to overcome this problem by imparting a pebbled surface
texture onto the half sole. The pebbled surface
reportedly enhances the adhesive properties of the sole
and facilitates application of a hot melt adhesive
thereto.
o~
Summ~ry of the Invention
A footwear assembly according to the invention
includes an uncured rubber upper, an uncured rubber
insole mounted on the upper, and a midsole mounted on
the insole. The midsole includes a midsole base and
suitable means for securing the base to the insole,
such as a vulcanizable rubber coating formed on the
base. The midsole base is made of a prefabricated
material which does not substantially undergo cross-
linking and which .etains its structural integrity
during vulcanization. The exposed outer face of the
midsole is disposed to receive an outsole. A vulcanized
footwear assembly may thus be formed by vulcanizing
such a footwear assembly, and a footwear product may
then be completed by securing an outsole to the midsole.
These and other aspects of the invention are described
in detail hereafter.
Brief Description of the Drawings
~igure 1 ls a perspective side view of a rubber
footwear product manufactured in accordance with the
present invention.
Figure 2 is a perspective tOp view of an
insole assembly according to the invention.
Figure 3 is a cross-sectional view taken along
line III-III of the Figure 2 insole assembly.
Figure 4 is a fragmentary perspective view of
a portion of an uncured rubber welt.
Figure 5 is a perspective top view of a
midsole shown in Figure 1.
Figure 6 is a cross-sectional view taken
along line VI-VI of the Figure S midsole.
A Figure 7 is a perspective bottom view of the
outsole shown in Figure 1.
Figure 8 is a perspective bottom ~iew of an
insole overlapped with an uncured rubber upper upon a
forming last in accordance with the invention.
Figure 9 is a perspective bottom view of an
uncured rubber welt assembled onto the footwear assembly
shown in Figure 8.
Figure 10 is a cross-sectional view taken
along line X~X of Figure 9 which comprises a cross-
sectional cut of the uncured upper, insole and welt
upon a metal las~.
Figure 11 is a perspective bottom view of the
uncured assembly of Figure 9 with the midsole attached
thereto.
?igure 12 is a cross-sectional view taken
along line XII-XII in Figure 11 showing the comple~ed
uncured assembly of the footwear product according to
the invention.
Detailed Description
Referring to Figure 1, the present invention
provides a rubber footwear product 1 comprising a
vulcanizate assembly 2 of unitary construction, which
as~embly 2 includes a rubber upper 3, a rubber insole 7
(occluded from view) and a rubber midsole (midsole
base~ 5, and an 6 separately secured to assembly 2.
Vulcanizate assembly 2 further includes a rubber welt 4
which improves the footwear product. The
intervulcanization of welt 4 with the other uncured
rubber components as illustrated, namely rubber upper 3
and rubber midsole 5, significantly enhances the
structural integrity, strength, water resistance and
wear properties of the resulting vulcanized footwear
product.
The present invention further provides a
method for the manufacture of a rubber footwear product
comprising vulcanizate assembly 2, which assembly 2
includes a rubber upper 3, insole 7 (see Figure 2),
54~
rubber welt 4, and midsole S, and an outsole 6 separately
affixed to midsole S of vulcanizate assembly 2.
The component parts and the method of manu-
facture of a footwear product according to the invention
may be more fully appreciated by reference to Figures
2-12. Figure 2 illustrates an insole 7 suitable for
use in the manufacture of the the footwear products
described herein. The illustrated insole 7 includes an
insole base 8 and an insole filler 9 added for insulation
and comfort purposes. Uncured rubber welt 4, further
illustrated in Figures 10 and 12, fits into a step 13
formed between insole base ~ and insole filler 9. Welt
4 may then become part of vulcanizate assembly 2, or
may be separately affixed to vulcanizate assembly 2. A
welt 4 constructed of a material selected from plastic,
including thermoplastics, rubber and other natural or
synthetic materials, may be separately affixed (e.g. by
an adhesive, sewing, etc.) to such a vulcanizate.
The uncured welt 4 is advantageously T-shaped
in cross-section or of a generally three-edged construc-
tion as shown, having a flat base 14 suitabl~ designed
to ~it onto step 13 and an upright, elongated, generally
centered rid~e i5 which interfaces with rubber upper 3,
as shown in Figure 4. The internally disposed surfaces
of welt 4 are preferably tapered to permit formation of
a smooth, contoured vulcanized surface with midsole S
and upper 3. Typically, rubber footwear vulcanizates
do not include a rubber welt. The outer edge of welt 4
may be suitably designed to coincide with the outer
periphery of midsole 5, as shown in Figure 12. As shown
in Figure 6, both the bottom and top surfaces of midsole
5 have a plurality of macroscopic projections 17 which
extend randomly outward from the surface of midsole 5.
Outer sole 6, shown in Figure 7, may be separately
secured to midsole 5.
~iQ2 ~
~ he manufacture of footwear product l may be
suitably carried out, as shown in ~igures 8-12, by
adhesively overlapping an uncured rubber upper 3 with
insole 7 at step 13 upon a forming last 10. The uncured
rubber welt 4 may then adhesively overlap uncured rubber
upper 3 and uncured rubber insole 7 on step 1~ about
the outer periphery of the shoe bottom, as illustrated
in Figures 9 and 10. Thereafter, a vulcanized rubber
midsole 5 is adhesively affixed to rubber welt 4 and
insole 7 tO provide an uncured assembly as shown in
Figures ll and 12. The uncured assembly may then be
vulcanized ~o provide intermediate vulcanized footwear
assembly 2 shown in Figure 1. The rubber upper 3 shown
in ~igures 10 and 12 comprises a liner 3a and an uncured
rubber outer portion 3b. Liner 3a serves to provide a
more comfortable footwear product, but may, if desired,
be omitted.
The interfacing components of vulcanizate
assembly 2 may be appropriately constructed from a wide
variety of natural and synthetic rubbers. Illustrative
synthetic rubbers include the polymers of diethylenicall~
unsaturated monomers alone or in combination with other
conventional ethylenically unsaturated comonomers.
Included amongst such ethylenically unsaturated monomers
are the straight and/or branched chain diolefins such
as isoprene, butadiene, chloroprene, diethylbutadiene,
and mixtures thereof. Conjugated dienes are preferred.
Copolymerized diethylenically unsaturated cyclic hydro-
carbons such as bicyclo-heptadienes, substituted cyclic
dienes (e.g. halogenated) and the like may also serve
as monomers or comonomers. Other conventional
ethylenically unsaturated comonomers may be suitably
copolymeri~ed with the diethylenically unsaturated
comonomers (especially with conjugated dienes) to impart
certain desirable attributes to the synthetic rubber.
Included amongst such comonomers are the lower alkenes
(e.g. Cl-C4 olefins such as ethylene, p~opylene, and
-
.
--10--
isobutylene), styrene and styrene derivatives, acryloni-
trile, acetylene, and other comonomers conventionally
copolymerized with dienes in the manufacture of synthetic
rubbers. Illustrative of such synthetic rubbers are
butyl rubber (isobutylene/isoprene copolymers), cis-
polyisoprene, neoprene (e.g. neoprene/acetylene co-
polymers), Buna N (e.g. butadiene/acrylonitrile copoly-
mers), ethylene, polypropylene/neoprene and butadiene/
bicycloheptadiene copolymers, and mixtures thereof.
Pursuant to the present invention, midsole 5,
as depicted in Figure S and 6, is especially adapted
for intervulcanization with the other uncured rubber
footwear components and affords a base (support surface)
for separately securing the outer sole 6 thereto. The
invention departs from conventional rubber footwear
manufacture not only by the nature and character of
midsole 5, but also by its use in the construction of a
rubber vulcanizate. The dimensional size and shape of
midsole 5 are advantageously designed to provide a base
for supporting outsole 6. Midsole 5 can be incorporated
into vulcanizate assembly 2 so that it extends outwardly
beyond a base 18 of rubber upper 3 as illustrated in
Figures 1, 11 and 12. Heretofore, such a midsoie
construction and appearance were commonly incorporated
into leather footwear products, but were inappoC~ite to
rubber vulcanizate manufacture. The outer edge of
midsole S may be suitably cut to substantially coincide
with the outer edge of the assembled welt 4. Midsole
base 5 should be constructed of a material capable of
withstanding the relatively high temperatures needed to
vulcanize the uncured rubber assembly illustrated in
Figures 11 and 12 into vulcanizate assembly 2, shown in
Figure 1, having a unitary construction.
Midsole S must be able to withstand the
vulcanization conditions needed to cure the uncured
rubber components into a vulcanizate without any
appreciable deformation o~ the size, shape, function or
25~
construction of midsole 5, that is, without melting,
shrinkage and other physical or chemical decomposition
or deterioration. Certain polymeric substances such as
thermoplastics which melt, deform or fail to retain
their structural integrity under vulcanization conditions
are unsuitable midsole materials. Thermoplastics
possessing sufficiently hi~h resistance to melting and
deterioration at or above vulcanization temperatures,
such as certain high molecular weight thermoplastic
materials (e.g. thermoplastic rubbers or thermoplastics
formulated with certain melt retardinq additives or
comonomers to prevent or inhibit thermal deformation or
decomposition, may be used to make midsole 5.
Crosslinked Dolymeric materials which are
resistant to thermal deformation and decomposition under
vulcanization conditions, which may be coated with an
uncured rubber at the midsole surface which interface~
with the other uncured rubber components of the assembly,
and which permit mldsole 5 to be intervulcanized therewith
into a vulcanizate of unitary construction may also be
used to make midsole 50 Rubber vulcanizates, including
those formulated with fillers, are especially well
adapted for use as a midsole base material. Filled
rubber vulcanizates may be prepared by uniformly admixing
together, for example, in a Branbury mixer, an uncured
rubber and filler or precursors thereof along with the
other desired conventional vulcanization additives, and
then forming the mixture by calendering, extruding, or
molding under vulcanizing conditions into a vulcanizate
composite of the desired midsole thickness. The pre-
formed vulcanizate may be milled, cut or stamped into
the desired size and configuration of the midsole
component.
The vulcanizate composite may contain a
particulate filler embedded and uniformly distributed
throughout the vulcanizate structure. Fibrous materials
or fibrous precursors derived from a variety of sources
5~
-12-
may be used as such a filler, including natural, synthetic
and fibrous particulate substrates which are organic or
inorganic. The following substances are exemplary of
such fibrous source materials: animal or proteinaceous
fibrous substances such as leather dust, silk, hair,
and wool; vegetable or cellulosic materials such as
cotton, flax, hemp, and jute, grain fibers or pulp such
as fibers or pulp of wheat, oat, bran, corn, soybean,
and cottonseed; wood fibers or pulp; regenerated ~ibrous
materials such as cellulose and proteinaceous materials;
synthetic fibers such as cellulose acetate; acrylic
fibers such as polyacrylonitrile; vinyl chloride/
acrylonitrile copolymers; inorganic or mineral substance~
such as asbestos; and mixtures thereof. Cellulosic
pulps such as those obtained from vegetative pulpy
substances are a particularly suitable fibrous source
material. Wood fibers such as wood flour, sawdust, and
buffer dust are especially well suited as a filler.
The vulcanized midsole 5 should be treated as
described hereafter on at least one face, and preferably
on both faces to enhance bonding of midsole 5 with the
other components. The inner midsole face which inter-
faces with the internally disposed portions of vulcanizate
assembly 2 should be chemically and/or mechanically
treated to permit the appLication and adherence thereto
of an uncured rubber coating 19. Chemical treatments
which permit an uncured rubber coating l9 to wet and
adhere to midsole 5, such as treatment with chlorinatin~
acids, may be used for this purpose. Similarly, roughing
or abrading the midsole provides a suitable surface for
coating the midsole face with an uncured rubber. As
~ illustrated in ~igure 6, such roughening tends to create
L~ a multiplicity of macroscopic projections 17 which are
firmly anchored within the adjoining vulcanizate matrix.
Such pretreatment permits the impregnating and coating
of the midsole inner surface 20 with an uncured rubber
substrate. Thus, the coated inner midsole surface may
5~
thereby be intervulcanized with the other uncured
components into a unitary rubber vulcanizate.
A similarly treated outer midsole surface
(e.g. roughened or ahraded) affords the means whereby
an outer sole may be separately affixed to the vulcan-
izate a~sembly 2. Abrading with a wire brush, a coar~e
emery wheel or coarse sandpaper (e.g. 60-80 grit) length~
wise and crosswise may be used effectively as a pre-
treatment for both of these surfaces. A milled rubber
composite manufactured and distributed by Monarch Rubber
Co., Baltimore, Maryland known as 1541 Apollo milled to
a thickness ranging from about 2 to about 4mm (preferably
about 3mm) and abrasively surface treated lengthwise
and crosswise has been found particularly effective for
mating midsole 5.
Midsole 5 cannot, by it~elf, be intervulcanized
with the other component parts of assembly 2. Coating
the internal surface of midsole 5 (i.e~, the surface
facing welt 4 and insole 7) with uncured rubber coat ng
l9 will typically impart sufficient adhesive tack to
permit adhesive bonding of midsole 5 to the uncured
rubber footwear assembly depicted in ~igures 11 and 12,
while providing a substrate which will intervulcanize
with the other uncured footwear components to provide a
unitary vulcanized product. Although the thickness of
coating l9 may vary, a coating of less than about 25
Mil. (i.e. 0.025 inch) thickness and most typically
less than 15 Mil. (e.g. about 5 to about 10 Mil ) will
generally be sufficient to permit the midsole to be
intervulcanized with the interfacing component~.
A satisfactory uncured rubber coating 19 upon
midsole 5 may be most effectively created by a two stage
coating process~ The first stage may be suitably
effectuated by initially coating the midsole vulcanizate
base 5 with an uncured rubber latex. Thi~ is followed
by a ~econd coat or overcoat of an uncured rubber
solution. Such a two stage coating proce~ tends to
-14-
significantly improve the wetting, penetration and
tenacity of the uncured rubber to midsole 5, and the
ultimate structural integrity of the vulcanizate.
The uncured rubber late~ may typically comprise
an uncured natural or synthetic rubber uniformly disper~ed
throughout a polar dispersant such as water. Such
latexes are typically formulated with conventional
emulsifiers or surfactant systems (natural or synthetic)
for emulsifying finely ~ivided or minute uncured rubber
particles throughout an aqueous carrier, along with
wetting a~ents, crosslinking agents (e.g. sulfur)~
tackifiers and other conventional curable rubber latex
additives. Conventional lower alkyl alcohols (e.g.
ethanol, propanol, etc.) are frequently added to enhance
the wetting and penetration of the uncured rubber
molecules and curing reagents into the porous interstices
of midsole 5. A commercially available natural rubber
latex sold as Northwest Latex 3003 (neutral), manufactured
and distributed by Northwest Coating Co., Oak Creek,
Wisconsin, has been found to be particularly effective
as a latex coating. Conventional coating techniques
such as spraying, brushin~, or dipping may be used to
uniformly apply the latex to the inner surface of mids-
ole 5. The volatile carrier (namely water) may then be
removed by conventional drying techniques including
air, oven, or vacuum drying conducted below the uncured
rubber vulcanization temperature. The dry latex coating
will form an uncured rubber film upon the inner surface
of midsole base 5.
An uncured rubber solution or non-polar
dispersion may then be applied onto the dry latex
coating. Such uncured rubber solutions or dispersions
typically include a suitable rubber solvent or non-polar
A dispersant, an uncured rubber component uniformly
di~solved or dispersed therein, plus cros~linking
x~
-15-
reagents, accelerators, wetting agents and other conven~
tional curative additives. Solvents such as gasoline,
benzene, chloroform, carbon tetrachloride, and carbon
disulfide tend to swell uncured and cured rubbers.
These solvents may be effectively utilized to enhance
the penetration of the uncured rubber solution and
vulcanizate reagents into the dry latex coating of
midsole 5, and to provide a more uniform coating of the
uncured rubber upon the surface of midsole 5. An
illustrative uncured rubber soLution (preferably of a
high bond strength and excellent relaxation propertie )
may be conveniently prepared by uniformly admixing, in
a cement churn, an uncured rubber stock, isopropyl
alcohol as a wetting a~ent, sulfur, hexane and heptane
as cosolvents, and other conventional rubber curative
additives (e.g. accelerators, activators, anti-oxidant~,
tackifiers, etc.) in conventional concentrations. The
uncured rubber solution may then be applied to the dry
latex precoat by conventional techniques such as those
mentioned above for applying the latex coating. After
the uncured rubber solution has been applied, excess
solvent may be removed therefrom by conventional means
such as vacuum, air or oven dryin~.
The uniformly coated vulcanizate midsole base
5 precoated with a dry latex and a solvent overcoat of
curable rubber provides an uncured rubber base which
readily intervulcanizes with the other uncured component
parts into a unitary vulcanizate assembly. The precoated
midsole thus described may be used to prepare the uncured
footwear assembly illustrated in Figures 11 and 12. As
is characteristic of uncured rubber stock, the uncured
coating lamina may be adhesively affixed to the adjacently
positioned uncured welt 4 and filler 9 of insole 7 upon
the last 10. The uncured a~sembly illuqtrated in Figure~
11 and 12 may then be vulcanized. Vulcanization causes
a melding together of uncured rubber components, including
uncured rubber coating 19, into unitary vulcanizate
`3
-16-
assembly 2. The interfaces between the component parts
are chemically altered into a unitary vulcanizate.
Coating of the outwardly facing face 22 of midsole 5 is
~enerally inadvisable unless it is desired to separately
apply a rubber outsole (@.9. for specialty soles such
as for golf shoes, running shoes, etc.) thereto, in
which case the uncured rubber coating therefor would
be applied after vulcanizate assembly 2 is made.
Vulcanizate assembly 2 of this invention
differs from conventional vulcanized rubber footwear by
the inclusion of midsole 5. Unlike the flexible and
internally disposed binders or fillers often used in
rubber vulcanizates as an internal interfacing component
with the outsole, a portion of midsole 5 can be designed
as an externally exposed component of the assembled
footwear product 1.
In the preferred embodiments of the invention,
midsole 5 provides an interfacing surface substantially
the same in size, shape and surface area as the
separately secured outsole 6. The contour of outer
surface 22 of midsole 5 may suitably match the contour
of the inner interfacing surface of outsole 6 to provide
a firm base therefor. Preferably, outer surface 22 o~
midsole 5 will be substantially flat, and cut to match
the outer periphery of outsole 6.
The present invention permits vulcanizate
assembly 2 to be combined with a multiplicity of outer
sole types. An intermediate vulcanizate article without
an outer sole may be initially manufactured, and a
speci~lty outer sole or fashion outer sole may then be
separately secured thereto. The unique constructions
and method of manufacture according to the invention
allow production of vulcanized footwear products having
a diverse variety of soles. Substantial inventory and
shipping cost savings may be realized by use of a
vulcanized footwear assembly adapted to separately
receive an outer sole. The vulcanized assembly may be
x~s~
conveniently shipped from the manufacturing site to
distant distributing sites, at which the desired outer
sole may be secured.
The outer midsole surface may be treated with
the latex precoat and uncured rubber solution overcoat
in the same manner a~ the inner midsole surface described
previously to permit an uncured outer sole to be affixed
thereto by vulcanization. Alternatively, an outer ~ole
vulcanizate of a similar composition and construction
as the midsole base may be coated with an uncured rubber
as defined herein and intervulcanized therewith to
provide the desired completed footwear product. The
outer sole 6 may be secured to the vulcanized base
footwear assembly 2 by an injection molding process
wherein a molten mass of an uncured rubber base, thermo~
se~ pla~tic or thermoplastic material i~ injected into
a formin~ ~old bearins the de~ired outer sole config-
uration onto vulcanizate assembly 2. The material is
then cooled to provide an outer cole 6 securely affixed
to assembly 2. A multitude of outer soles differing in
color, design and function may thereby be firmly secured
to vulcanizate assembly 2. The present invention
obviates the need for manufacturing the completed foot-
wear product in a single vulcanization step as is
nece~sary with conventional processe~ for manufacturing
vulcanized rubber footwear.
Another important attribute of the present
invention is its ability to allow an outsole to be
adhesively applied to the vulcanized ba~e footwear
product. A multiplicity of outer soles of differen~
compositions can be adhesively secured to midsole 5 of
vulcanizate assembly 2. The pretreated outer surface
of midsole S, as mentioned above, affordq a secure base
for applying an adhesive composition to the mid~ole
surface and for firmly affixing or anchoring outer ~ole
6 to vulcanizate assembly 2. In contra~t to conventional
rubber footwear vulcanizate~ which are normally discarded
2~
-18-
when the outer sole becomes worn and unfit for further
use, the present footwear products can be repaired by
simply replacing the worn outer sole with a new outer
sole. The present invention can also provide a unitary
vulcanizate assembly 2 comprising a cured rubber upper,
rubber insole, rubber welt and midsole in combination
with an outer sole of a diferent composition securely
affixed thereto. Rubber footwear product~ of a lighter
weight, embodying significant advances in style, design
and utility, are made possible by this aspect of the
invention.
Outsoles made rom a variety of natural and
synthetic materials may be used in footwear products 1
according to the present invention. Vulcanizate assembly
2 may be secured to a wide variety of soles presently
used in the construction of other footwear products,
many of which are unfit for use in conjunction with
conventional vulcanized rubber footwear products. Outer
sole 6 may be made from naturally occuring materials
such as natural ru~ber crepe and leather, as well as
synthetic thermoplastic or thermoset plastics such as
polyurethane, ethyl vinyl acetate, polyolefins, poly-
vinylchloride, thermoset and/or thermoplastic foams
(e.g. macroscopic and micro-cellular) of an open or
closed cellular construction, and combinations thereof.
The present invention affords a means for substantially
reducing overall footwear weight because outsole 6 need
not be made from vulcanized rubber, which has a specific
gravity normally within the range of 1.2 - 1.3 depending
upon additives. An outsole 6 having a specific gravity
significantly less than a cured rubber, e.g. 0.~,
particularly le~s than about 0~6, as well as foamed
outsoles having a specific gravity less than about 0.5
often ]ess than about 0.4) may be affixed to vulcanizate
assembly 2.
~ ~6~25i6
The most appropriate adhesive for securing
outsole 6 to midsole 5 will depend upon the composition
and adhesive compatibility of the interfacing surface
of outsole 6 with the adhesive. The composition and
construction of midsole S is generally compatible with
a broad range of adhe~ives commonly used to secure
outsoles in conventional shoe manufacture and repair.
Exemplary adhesives include thermoplastic hot melts,
contact cements, polyurethane cements, epoxy resins,
animal glues, rubber cements (e.g. neoprene cements),
and mixtures thereof. Neoprene and polyurethane cements
have been found particularly effective for rigidly and
permanently securing an outsole 6 to midsole 5.
